1. Field of the Present Invention
The present invention relates to an air supplied respiratory device, and, more particularly, to a breathing regulator having a non-linear positive pressure spring.
2. Background
A known respiratory device is the Self-Contained Breathing Apparatus (SCBA). SCBA's are commonly worn by individuals when carrying out activities in hazardous environments, such as when fighting fires and in other smoke- or gas-filled environments, in order to provide the wearer with breathable air. The SCBA is comprised of a number of assemblies including a cylinder and valve assembly for storing breathing air under pressure, a full facepiece assembly, one or more pressure reduction assembly including a breathing regulator, a harness and backframe assembly for supporting the equipment on the back of the wearer, and a remote gauge indicating cylinder pressure.
Although a number of standards and requirements with respect to such equipment have existed over the years, these standards and requirements continue to become more demanding. For example, the NFPA, an independent consensus group supplying advisory services, data collection, analysis and research services, all related to fire prevention and fire safety, established a standard in 1971 for Protective Equipment for Fire Fighters. In 1981, NFPA specified National Institute for Occupational Safety and Health (NIOSH)/Mine Safety and Health Administration (MSHA) approved Self-Contained Breathing Apparatus (SCBA) with a minimum rated service life of 30 minutes and open-circuit SCBA was required to be positive pressure. Open-circuit SCBA refers to a SCBA in which exhalation is vented to the atmosphere and not rebreathed. There are two types of open-circuit SCBA: negative pressure or demand type, and positive pressure or pressure demand type. Positive pressure SCBA was required after 1981 and is the type in which the pressure inside the facepiece, in relation to the pressure surrounding the outside of the facepiece, is positive during both inhalation and exhalation when tested by NIOSH in accordance with 42 CFR 84, Subpart H.
There are a number of other standards that exist with respect to air supply respirators. Another such established test procedure is the National Institute for Occupational Safety and Health (NIOSH) 42 CFR Part 84. Certification of an SCBA for use in chemical, biological, radiological and nuclear (“CBRN”) environments is a function of NIOSH Approval of Respiratory Protective Devices. NIOSH is part of the U.S. Department of Health, Education & Welfare and establishes the basis for testing (i.e., flow rates, weight, etc.) and certification of respiratory equipment.
Another test standard is the European Standard, EN 137, entitled “Respiratory protective devices: self-contained open-circuit compressed air breathing apparatus.” The European test standard's function is similar to the NFPA in the United States. It demonstrates that the need for effective respiratory equipment is a global concern.
One of the most critical assemblies of the SCBA is the breathing regulator, also commonly known as a second stage regulator. A function of the breathing regulator is to reduce the air pressure from the incoming supply hose to a pressure that is low enough (0 to 3.5 inches water column) to be breathable by a person. This pressure reduction creates a pressure drop from a reservoir of high pressure to a reservoir of low pressure, and modulates flow to the user.
Another function of the breathing regulator is to maintain a pressure inside a mask comprising a full facepiece assembly above the ambient pressure. Maintaining inside pressure prevents smoke or other contaminants encountered in an imminent danger to life and health (“IDLH”) environment, such as carbon monoxide and the like, from entering the mask when a user is inhaling. Masks and/or regulators that are specially designed for use in CBRN environments may also be capable of preventing contaminants such as sarin (GB) or distilled sulfur mustard (HD) from entering the mask, but conventional (non-CBRN) masks may generally not be employed for that purpose. When a user exhales, the pressure inside the mask increases until a vent opens releasing expired air. Static pressure above ambient pressure is always maintained.
Exhalation pressure in conventional breathing regulators is generally approximately 2.5 inches water column. The lower the exhalation pressure, the easier it is for a user to exhale. Accordingly, lowering the exhalation pressure allows a user to breathe easier.
Many conventional breathing regulators make use of a spring or the like to maintain pressure within the mask. The spring biases the exhalation valve assembly closed. During inhalation, air is being drawn into the mask, and little or no force is exerted against the exhalation valve assembly, so the exhalation valve assembly remains closed. However, during exhalation, air pressure of the exhaled breath applies a force against the exhalation valve assembly. If the force is great enough to overcome the force applied by the spring, then the exhalation valve assembly is opened and exhaled breath is exhausted therethrough. Accordingly, in order to breathe out, a user must generally exhale with enough force to overcome the biasing force of the spring for a period of time long enough to complete the exhalation phase of the breathing cycle.
A significant drawback, however, to known prior art breathing regulators is the type of spring utilized thereby. Such regulators make use of a “linear”-type spring. The term “linear” as used in the context of the present invention means that the deflection of the spring is directly proportional to the force applied to the spring throughout the normal range of operation of the spring. Unfortunately, in order to keep the exhalation valve assembly open far enough to permit exhaled air to pass through the breathing regulator quickly enough to enable the user to breathe at a comfortable pace, the user must exhale strongly enough to generate a relatively high pressure in the regulator. This, in turn, requires a relatively high level of exertion on the part of the user in order to generate this pressure. Such exertion may not be comfortable for even the casual user, but the effort required to breathe is even more significant when the user is engaged in the elevated levels of physical activity common to many SCBA users.
Thus, the present invention intends to overcome the problems associated with the use of existing breathing regulator designs utilizing a linear spring, while at the same time successfully meeting the standards for respiratory equipment certification.